1. Field of the Invention
This invention relates generally to a fuel cell system and, more particularly, to a fuel cell system that employs wax elements as passive control devices to control certain system components, such as coolant fans, coolant pumps and valves in the system.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. A hydrogen fuel cell is an electrochemical device that includes an anode and a cathode with an electrolyte therebetween. The anode receives hydrogen gas and the cathode receives oxygen or air. The hydrogen gas is dissociated in the anode, with the aid of a catalyst, to generate free hydrogen protons and electrons. The hydrogen protons pass through the electrolyte to the cathode. The hydrogen protons react with the oxygen and the electrons in the cathode, with the aid of a catalyst, to generate water. The electrons from the anode cannot pass through the electrolyte, and thus are directed through a load to perform work before being sent to the cathode. The work acts to operate the vehicle.
Proton exchange membrane fuel cells (PEMFC) are a popular fuel cell for vehicles. The PEMFC generally includes a solid polymer electrolyte proton conducting membrane, such as a perfluorinated acid membrane. The anode and cathode typically include finely divided catalytic particles, usually platinum (Pt), supported on carbon particles and mixed with an ionomer. The combination of the anode, cathode and membrane define a membrane electrode assembly (MEA). MEAs are relatively expensive to manufacture and require certain conditions for effective operation. These conditions include proper water management and humidification, and control of catalyst poisoning constituents, such as carbon monoxide (CO).
Many fuel cells are typically combined in a fuel cell stack to generate the desired power. The fuel cell stack receives a cathode charge gas that includes oxygen, and is typically a flow of forced air from a compressor. Not all of the oxygen in the air is consumed by the stack and some of the air is output as a cathode exhaust gas that may include water as a stack by-product. The stack also receives a hydrogen anode gas. A cooling system is generally required to remove heat from the stack generated by its operation.
The known control systems for a fuel cell cooling system employ sensors, powertrain controllers and actuators to perform the control. It would be desirable to eliminate some of these devices to reduce system complexity, weight, etc.
Wax element devices are known in the electronics industry as simple electrical switching devices. It would be desirable to employ such wax element devices to provide passive control in fuel cell systems.